As the size of structures in semiconductor devices and other similarly manufactured devices continue to shrink, the demand for tighter tolerances increase. One way to ensure that fabricated structures meet allowable design tolerances is to have accurate characterizations of the processing tools used in each processing step. The characterization of each processing tool is important, because variation of the processing conditions within a tool may affect the substrate being processed. For example, in etching and material deposition processes it is important to know how the processing conditions will affect the rate of change of the thickness of a material layer. However, even within a single processing tool there may be variations in the rate of change of the thickness of the material. For example, in processes utilizing a plasma, such as plasma enhanced chemical vapor deposition (PECVD), the thickness of a material layer may have a different rate of change in an area proximate to the edge of the substrate compared to an area located near the center of the substrate.
Currently, without invasive modifications to the processing chamber of a tool, only the average rate of change may be calculated. After processing a substrate, the material layer may be measured to determine the total change that occurred. Then the average rate of change may be calculated by dividing the total change in thickness by the total processing time. In order to determine if there are variations across the substrate as a result of the processing, then the measurements and calculation must be performed at multiple locations on the substrate as well. This process may provide information regarding the uniformity of the change in a surface, but it lacks the ability to provide temporal information. In addition to not being able to provide temporal information, this process is time consuming because it requires both a processing operation and a separate measurement operation. Alternative efforts to provide temporal information for the rate of change of a material layer have utilized a laser beam to measure the thickness of a material layer through polarization or spectral reflectance. While this may provide the temporal information, its use if often limited to research facilities due to the extensive modifications needed to the processing chambers.
Therefore, there is a need in the art to provide methods and apparatuses for measuring the rate of change of a material layer while it is being processed without the need for extensive modifications to the processing chamber of the tool.